1. Field of the Invention
The present invention relates to an infrared sensor, and more particularly to an infrared sensor to be incorporated into a burglar alarm or the like and used for detecting human beings and other living organisms.
2. Description of the Related Art
FIG. 14 is a perspective view showing one example of conventional infrared sensors, and FIG. 15 is an exploded perspective view thereof. The infrared sensor 1 comprises a metal stem 2 having a step portion 2a, called an islet. Through-holes are formed in the metal stem 2 and three lead terminals 3a, 3b, 3c are passed through the through-holes. The lead terminals 3a, 3b are sealed with insulating glass 4 having nearly the same thermal coefficient of expansion as the metal stem 2, and the lead terminals 3a, 3b are fixed and at the same time electrically insulated from the metal stem 2. The ground lead terminal 3c is fixed by soldering, pressing in, etc. so as to be electrically connected to the metal stem 2. Usually, the metal stem is formed of a hermetic sealing type metal stem used for operational amplifiers.
A circuit board 5 is arranged on the step portion 2a of the metal stem 2. The circuit board 5 is formed of an insulating material. A conversion circuit for converting electric charge generated in a pyroelectric element (to be described later) into a signal is formed on the circuit board 5 using, for example, a field-effect transistor (FET) 6. This conversion circuit is connected to the lead terminals 3a, 3b, 3c which protrude from the step portion 2a of the metal stem 2. Further, a pyroelectric element 8, connected to the conversion circuit formed on the circuit board 5, is arranged on the circuit board 5 through supports 7. A metal cap 9 covers the pyroelectric element. A window is formed in the cap 9, and an optical filter 9a is attached to the window. Infrared rays are conveyed to the pyroelectric element 8 through the optical filter 9a. The cap 9 is fixedly mounted on the stem 2 by electric welding. The metal stem 2 and cap 9 electro-magnetically shield the conversion circuit and suppress the effect of external noise on the conversion circuit.
In this infrared sensor 1, electric charge is produced in the pyroelectric element 8 by infrared rays which enter through the window portion of the cap 9 and the electric charge is converted into a signal by the conversion circuit. By measuring of the output signal from the infrared sensor 1, the movement of human beings and other living organisms can be detected. In order to thermally and electro-magnetically make good use of the pyroelectric effect of the pyroelectric element 8, hermetic sealing is provided by the metal stem 2 and cap 9 and the effect of disturbance noise is restrained by electromagnetic shielding.
There has been recently arisen a large demand for burglar alarms and the like using this type of infrared sensor for home use. Such burglar alarms must be inexpensive for home use. However, the conventional infrared sensor is expensive, as the stems used in such infrared sensors are expensive because they are produced by a precise manufacturing method. Further, the lead terminals which protrude inside the stem create inductance components because of the effect of external high-frequency noise and the noise induces a voltage in the high-impedance system to cause failure of the infrared sensor.
It is therefore an object of the present invention to provide an infrared sensor which can easily be produced, which is a stable high-impedance system substantially unaffected by noise, and which exhibits a small incidence of failure.
The infrared sensor comprises a stem, a pyroelectric element arranged on one side of the stem, a conversion circuit for changing electric charge generated in the pyroelectric element into a signal, and a plurality of lead terminals formed so as to be extended to the other side of the stem and electrically connected to the conversion circuit. The lead terminals are fixed to the stem by caulking.
In this infrared sensor, the stem is formed with insulating material, and a conversion circuit is formed on the surface of one side of the stem. Further, the stem of one layer or multilayer construction is formed, and at least on one side surface of the stem the grounding electrode for electro-magnetic shielding is formed.
Moreover, a case made up of conductive material which is to cover one side of the stem, is preferably included, and the case and stem are securely fastened and sealed with conductive resin adhesive.
By caulking the lead terminals (i.e., deforming them the through holes through which they extend), the lead terminals are fixed to the stem and the through-holes for the lead terminals formed in the stem are sealed. Further, by caulking the lead terminals, the lead terminals do not extend on one side of the stem and accordingly it is unlikely that voltages will be induced in the lead terminals inside the stem by disturbance noise.
When the stem is formed by an insulating material and a conversion circuit is formed on one surface of the stem, it becomes unnecessary to utilize another circuit board and the size of the infrared sensor can be reduced.
Furthermore, by forming the grounding electrode on the stem, it is possible to achieve electro-magnetic shielding thereby reducing the effect of disturbance noise. Moreover, the grounding electrode is able to be formed on one side or both sides of the stem, and when the stem is made up of multiple layers, the grounding electrode can be formed in one layer or a plurality of layers of the stem.
By providing a case over one main surface of the stem, sealing the case and stem by conductive resin adhesive, and sealing the stem by caulking the lead terminals, the pyroelectric element and conversion circuit are hermetically sealed. By forming the cap from conductive material and by forming a grounding electrode on the stem, an excellent electro-magnetic shielding effect is provided.